Biomedical nanoparticles promise a revolution in therapeutics and imaging. Nanoscale particles that include cerium and oxygen can be referred to as cerium oxide nanoparticles (CNPs), or “nanoceria” represent a case in point. These materials can be scavengers for reactive oxygen species (ROS), which is their desired antioxidant activity for biomedical applications in cancer therapy, neuroprotection, and other conditions. However, depending on the synthesis, they may instead be toxic materials leading to oxidative stress, or they can be biomedically inert. Their activities vary from batch to batch, change over time, and there are no known methods to stop the time-dependent aging processes that alter the desired biomedical properties. The fact that nanoparticle properties vary with synthesis conditions, and then vary in properties with time after synthesis, represents a major obstacle to the translation of nanoparticle therapeutics into practice. Indeed, even biomedical research with such nanoparticles is hampered due to poor reproducibility of nanoparticle materials. Solutions are needed to overcome the problems associated with general biomedical nanoparticle synthesis.
Biomedical nanoparticles described generically as cerium oxide nanoparticles, or nanoceria, are not strictly CeO2. Rather they are nanoscale particles that include cerium and oxygen, where the cerium may exist as Ce III or Ce IV or as a mixture of Ce III and Ce IV. The oxygen may be present as oxyanions or hydroxide anions, for example. In some compositions, oxygen can be present as peroxy species. For biomedical efficacy, it is believed that Ce III must be present as part of the nanoparticle to obtain antioxidant activity, and that small irregular nanoparticles are ideal. Biomedical nanoparticles often have more cerium III than cerium IV.